1. Field of the Invention
The present invention relates to a planar micro-actuator in which feed of power to slider electrodes is facilitated, the micro-actuator having, remarkably improved, reliability. This invention is also directed to a micro-actuator wherein a change in capacitance is used to produce a driving force.
2. Description of the Prior Art
In a planar micro-actuator utilizing a change in capacitance to generate a driving force, a capacitor must be formed physically by disposing electrodes on the opposed surfaces of a slider and the cooperating stators. Since the electrodes on the stator are fixed electrodes, they can easily be connected to an external power supply. However, since the electrodes on the slider move with the movement of the slider, their connection to an eternal power supply is extremely difficult.
For example, if a thin metal wire is used to connect the slider electrodes to the external power supply, viscous resistance to the movement of the slider due to the connection wire(s) acts as an adverse influence and since the actuator must always be connected to an external system, an integrated sub-system cannot be accomplished. These problems remarkably impede the realization of a micro-machine consisting of a combination of sub-systems, each sub-system comprising a planar micro-actuator.
A previously proposed method for solving the above-described problem does not use change in capacitance but uses a dielectric material having a dielectric constant and electric conductivity suitable for driving, such as plastic film, paper, etc, as the slider material, and utilizes electrostatic induction without disposing electrodes on the slider. In comparison with a micro-actuator which relies upon a capacitance change, however, a micro-actuator of this electrostatic induction type is not a synchronous motor because driving is effected only under the state where slip exists, and the driving force is physically small because the slip is not zero. For these reasons, this prior art method is not an actual solution.
Other problems of long standing in the art are as follows. Driving energy is stored in a gap between a slider and stators and because the lines of electric force change markedly in accordance with the gap, physical means for making the gap uniform is necessary. Further, a structure for reducing a contact area is necessary so as to reduce Coulomb friction between the slider and the stator. Furthermore, since any deviation of opposed electrodes between the slider and the stators in directions other than the moving direction of the slider, markedly reduces the driving force of the micro-actuator, a structure for preventing such deviation is also required.
Generally, a three-phase D.C. rectangular wave or A.C. traveling wave is used for driving a planar micro-actuator. Referring to FIG. 5, in order to achieve three-phase driving, a large number of electrodes 2 connected laterally to three-phase electrodes represented by symbols .phi.1, .phi.2 and .phi.3 and extending longitudinally, are required. The electrode .phi.2 is connected to the electrodes on the sides thereof through via-holes 1.
In the conventional electrode layout for three-phase driving described above, however, formation of the through-holes 1 and connection by thin wires are necessary, and at least two conductor layers are necessary for forming the through-holes. Further, since such an electrode arrangement is provided on both slider and stator sides, reduction of the weight of the slider is difficult.